HElP me get 10 points pls?

Well we bought a shih zu cross poodle on monday and since she came home she has been coughing we took her to the vet and she said that she needs antibiotics, however she is drinking the medication and still has coughs could anyone help please why does this happen all of a sudden when she is sleeping or sittin she coughs as if she is going to vomit but she doesnt!! she is 3 months old